The shoulder is a very unique joint in the human body having the greatest range of motion while being least stable than other large articular joints. FIGS. 1A-B show different aspects of a human shoulder joint anatomy. There are four separate joints that make up the shoulder; the main one is the glenohumeral joint formed by the humerus head or “ball” 102 and a socket on the scapula denoted as the glenoid 104. The glenoid itself defines a glenoid fossa 120 which is very shallow and small (covering at most only a third of the humerus ball), also relative to other joints in the body, and fitting is accomplished by the presence of the glenoidal labrum 114, a fibrocartilaginous rim attached around the margins of the glenoid fossa/cavity 120 which substantially deepens the glenoid cavity and protects the edges of the bone. The labrum is triangular-like in cross section with its base fixed to the circumference of the cavity. Articular cartilage 110 covers the end extension of the humerus ball (as well as, 112, in the glenoid cavity), a thin layer of a slippery material having a stiff rubbery consistency, mainly serving as a shock absorber (or cushion) and provides an exceptionally smooth surface for an easy relative motion between the ball and socket members. In one aspect the glenohumeral joint differs from the hip joint (the second ball-and-socket type joint in the human body) by the fact that the articular cartilage is substantially thinner and the shocks and impulses and forces applied to it have different amplitudes and different temporal profiles. The glenohumeral joint is maintained in-place by a joint capsule 118 formed by a group of enveloping ligaments. The synovial membrane 116, or synovium, is the inner layer or lining of the joint capsule. It is composed of connective tissue, and secretes a lubricating fluid named synovial, a viscous non-Newtonian fluid which reduces friction to facilitate motion between the joint members in a synovial cavity 106.
The unique combination and correlating configuration of the glenohumeral joint members, namely the capsule, the cartilage and the synovium, allows these incomparable characteristics of the shoulder with respect to other articular joints in the human body. Any disorder of at least one of the joint members may cause dysfunction and at least severe discomfort and pain sensation to the patient. A common disorder is the glenohumeral joint osteoarthritis, or degenerative joint disease, where the cartilage gradually thinned and eventually completely worn out. Besides osteoarthritis, which is the most common type of arthritis, there are also other related illnesses such as rheumatoid arthritis. Synovium can also become irritated and thickened in conditions such as rheumatoid arthritis. Adhesive capsulitis, also known as “frozen shoulder”, is a disorder in which the shoulder capsule becomes inflamed and stiff, greatly restricting motion and causing chronic pain. Frozen shoulder may be caused by trauma or injury, and probably involves an autoimmune component and/or indicated in lack of synovial fluid.
The more severe cases of glenohumeral joint disorders are usually treated with surgical intervention known as shoulder arthroplasty, in which the glenohumeral joint or only the humerus head is partially or completely removed and replaced with prosthesis. Arthroscopic introduction of healing regenerative substances and matrixes (such as the Graftjacket®, an acellular dermal matrix allograft manufactured by Wright Medical Group, Inc.) was also tested and found efficient in some cases.
The following examples describe several initiatives to treat general articular joints disorders, though not specifically specified or adapted for the shoulder glenohumeral joint.
European patent publication number 0507645 to Bouvet, the disclosure of which is fully incorporated herein by reference, describes an implant comprising a leak tight envelope made of a flexible, non-elastic material and a fluid incompressibly filling up the envelope, the envelope is capable of being interposed between the two parts of a joint which are to move with respect to each other, and it is in contact with both these parts. According to this document, the implant is intended for reducing production of particles due to wear of joint prostheses after full or partial arthroplasty. Its incompressible character is especially intended for maintaining the two parts of the joint (for example, the “ball” and “socket” members) at a constant distance while allowing natural joint movements without friction of the surfaces in contact. The proposed exemplary embodiment was focused on the coxo-femoral or “hip” joint, which, it should be noted, is mechanically, anatomically, medically and functionally different from the shoulder joint.
U.S. patent application Ser. No. 10/865,238 to Ku et al., the disclosure of which is fully incorporated herein by reference, describes a prosthesis for placement into a joint space between two or more bones. The prosthesis includes a body formed from a pre-formed solid one piece elastomer, wherein the elastomer is formed from a synthetic organic polymer that is biocompatible and has a modulus of elasticity and a mechanical strength between 0.5 MPa and 75 MPa. The body having a shape contoured to fit within a joint space between the femoral condyle, tubercle, and tibial plateau without any means of attachment.
U.S. patent application Ser. No. 12/259,907 to Philippon et al., the disclosure of which is fully incorporated herein by reference, describes a device for accessing and distending a joint comprises a distraction structure having a generally tapered distal portion adapted to penetrate a tissue region and create an access space within a joint. The distraction structure also includes a lumen extending from a proximal surface to a distal portion. The device further includes a distention structure deployable through the lumen and adapted to exert a force between a first joint surface and a second joint surface and create a working space. The distention structure may, in some embodiments, include an elongate member having a proximal end, a distal end, and a lumen extending along at least a portion of the length of the elongate member, a first expandable region deployable from a first substantially collapsed position to a second substantially expanded position, the first expandable region adapted to exert a force between the first joint surface from the second joint surface.
US patent publication 2009/0187252 describes an implant for relieving damaged areas of the surfaces of hip or shoulder joints from stress. The implant is cup-shaped or cap-shaped, rests in the socket by means of a convex external face and sits in the condyle by means of a convex external face in the implanted state. The implant comprises at least two articulation layers which are movable relative to each other and encompass articulation surfaces that face one another in the implanted state. Also described is an implantation method where the implant is pushed, using fluid through a channel that is drilled in the trochanter and femoral head, in to a joint space of a hip joint.